In general, a microlens installed in an image sensor is manufactured using a photosensitive resin composition.
In such a microlens, in general, required properties include the reduction of coloring by high-temperature heating and the prevention of a reduction in transparency (resistance to heat discoloration) and being formed in a favorable patterned shape (patterning capability) as well as transparency, heat-resistance, and solvent-resistance. As the photosensitive resin composition used herein, a photosensitive resin composition for forming a microlens that contains a hydroxystyrene-based copolymer or polyhydroxystyrene has been conventionally known.
A photoresist composition, a composition for forming an anti-reflective coating, and a material for forming a resist protection coating for immersion lithography that each contain a maleimide-based copolymer have been developed (Patent Documents 1 to 4). For the purpose of the development of insulating films for display devices such as liquid crystal displays (LCDs) and organic electroluminescent displays, a method for forming an insulating film for a display device that employs a radiation-sensitive resin composition containing: an alkali-soluble copolymer containing indene, maleimide, and N-substituted maleimide, a 1,2-naphtoquinone diazide compound, and a cross-linking agent has been developed (Patent Document 5).
Furthermore, being extremely excellent in compatibility with polyfunctional (meth)acrylate and having favorable alkali solubility, and for the purpose of being used in various uses in which such characteristics are required, a maleimide-based copolymer that is characterized by containing a monomer structural unit of unsubstituted maleimide origin, a monomer structural unit of styrenes origin, and a monomer structural unit of (meth)acrylic acid origin has been developed (Patent Document 6).
However, these prior documents do not have an object of providing a use as a photosensitive resin composition for forming a microlens and do not suggest any specific means or effect for the application of a copolymer having an unsubstituted maleimide structural unit and a vinyl ether structural unit to a photosensitive resin composition for forming a microlens.
A radiation-sensitive resin composition that contains [A] a polymer of (a1) unsaturated carboxylic acid and/or an unsaturated carboxylic acid anhydride, (a2) an epoxy group-containing unsaturated compound, (a3) a maleimide-based monomer, and (a4) other olefin-based unsaturated compounds and [B] a 1,2-quinonediazide compound has been disclosed (Patent Document 7). However, although it is described that the radiation-sensitive resin composition reported in this document can obtain high radiation-sensitivity and easily form a patterned thin film having excellent solvent-resistance, heat-resistance, transparency, and resistance to heat discoloration, the document does not suggest any specific shape accuracy of a pattern formed of the composition. Furthermore, it does not describe unsubstituted maleimide as the maleimide-based monomer.